Experiments on 24-hour cycles of snesory performance accuracy are proposed with an emphasis on free-running circadian rhythms under constant environmental conditions, and entrainment patterns in the presence of daily periodic dues. The data will extend previous analyses of general behavioral activity rhythms to psychophysical detection behavior under the control of weakly discriminable stimuli. Using pigmented Lewis B/N rats, performance in continuous detection test sessions will be analyzed as a function of time. Circadian periodicity in the discriminability of monochromatic visual stimuli, auditory pure tones and electrical brain stimuli will be studied. Entrainability of the rhythms to strick 24-hour periodicity will be attempted to both visual and non-visual cyclic entrainment agents. The effect of lesions of the hypothalamic suprachiasmatic nucleus will be studied to assess possible differential control mechanisms in circadian motor activity and (visual) sensory functions. the psychophysical method will be based onthe human yes-no paradigm, with correct detections reinforced by brain stimulation and errors producing brief timeouts. Reciever operating characteristics will be generated as a function of time, to specify circadian influences on response bias and detectability. bias-free measures of discriminability, plotted as a function of time, will be subjected to mathematical waveform analyses to specify period, phase and amplitude characteristics of the spuchophysical performance for comparison with circadian motor activity data.